Measurement of echoes



Feb 25, 1930. J. P. sATTl-:RTHWAITE ET AL 1,748,192

MEASUREMENT OF EGHOES Filed oct. 3o, 1928 ATTORNEY Patented Feb. 25, 1930 large Iofhces.

f UNITED A,Smit11S ,Peirlzlrrf OFFICE .ros'HUA P. SATTERTHWAITE, oF WEsTFIELn, NEW JERSEY, AND JAMES E. DINGMAN, 0E BROOKLYN, NEW YORK, AssrGNoRs To AMERICAN TELEPHONE AND TELEGRARH V.c:o`1v1PA1t\TY, A CORPORATION 0E NEW YORK MEASREMENT or EcHoEs Application mea october 30,1928. serieu No. 316,016.

, y.This invention relates tothe measurementlof. echoes, and more yparticularly to the measurement of echoes in long repeated signal transmissioncircuits, vwhich echoes may Vbe of such delay and volume as to affect seriously the signal transmission. n

`One object of the invention is the measurement of near-end or talker echoes with respect to the delay or transmission time of vthe echoes.

Another" object of the invention is the measurementy of the strength or volume of ,the echo waves returning to the near-end.

rA further object is the measurement of the delay and the strength of the listener echoes atthe far-end. 'A Vstillfurther object of the invention is the measurement of echoes as indicated above in a simple and practical manner suitable for useat transmission desks or testboards in According to one feature `of the invention, a commutator arrangement at the talker end is `associated with a source of tone and a receiver, and is adapted to indicateV in simple rfashion the time elapsing between the send- ;ing into the ycircuit of alternating current impulses and the arrival ofthe echoes at the talker point. v, i f

, In accordance with'a second feature of the invention, va potentiometer is employed at the talker end, and avswitchfassociated with the receiver is adapted to be thrown to two positions alternately to give a comparison between the volume of the outgoing impulses and the volume of the echoes.

' In accordance with a third featureof the invention, there is employed at the listener point apparatus somewhat similar to that used* at the talker end of the circuit for indieating the strength of the listener echoes and f the delay between the arrival at the listener ing apparatus employed at the near-end and the apparatus used atthe far-end for measuring the list-ener echoes.

A two-way transmission circuit is shown extending from point W', which is understood tobe the near or talker end'of the circuit, to point E, which is the far or listener end. The transmission line L, as is indicated in the drawing, includes a, plurality oftwoway repeaters.

At point W there is shown a commutator arrangement having two rotatable arms A1 and A2 connected to a common shaft and designed to be rotated by the motor M1 or by other suitable driving apparatus. rThe arm A1 1s associated with face F1, which'has an outer ring ORl and an inner ring IR1. Carried on the arm A1 are two brushes Bland B1', the former associated with the outer ring yBrushes B2 and B2 are carried on the arm A2 vandare associated respectively with the outer ring 0K2 and the inner ring 1K2. These brushes are yelectrically interconnected. The

outer ring @R2 is segmented, including the short segment S2 insulated from the rest of the ring. This face F2 carries an index arm Il, which is associated 'with a scale SG1.

' As is indicated on the drawing, the com- Vmutator face F1 may be fixed, while the commutator face F2 is adapted to be rotated with respect to face F1. v

A hybrid coil H is associated with the transmission line L and has connected to its net terminals a potentiometer P1. Resistances r1 and r2 are connected as shown in the drawing. An oscillator O or any other suitable source of tone is associated with the commutator face F1, as indicated, and a telephone receiver Rl is associated with the face F2, the connections of this receiver being controlled by a switchSWl.

The commutator faces F1 and F2 are ad- CTI justed so that with face F1 in its fixed position and face F2 in such a position that the indicator arm I1 points to zero on the scale SG1, brush B1 will make Contact with segment S1 and brush B2 will make contact with segment S2 atthe same time. When the commutator arms are 'rotated at a suitable speed, intermittent contact is made between brush lB1 and segment S1 andan interrupted tone,

for instance a 1,()O0-cycle tone,vis sent out over the line L. After a brief lapse of time a certain amount of the tone sent out over the line will return to the point W as reliected current or echo. The strength of the echo will, of course, depend upon the'degree of unbalance at the various repeater points, and

each component returned to the measuring definite fraction of the outgoing impulse fromV point will have a delay or transmission time dependent upon the distance between the measuring and the point of unbalance. lf the receiver R1 is connected between the line and the commutator face F2. by the throwing` of switch SWL to the right, the returned currents will be detected in the receiver. The face F2 is now rotated with respeet to face F1 until echoes are heard in the receiver`R1. Since the face F1 is fixed at a normal position, and since the indicator I1 carried by the face F2. travels over the scale SG1, the'displacement of face F2 with respect to face'F1 is clearly indicated. From this displacement and from the speed of rotation of the commutator arms it is, of course, a

' vsimple matter to determine the time which it has taken the waves from the oscillator O to travel out over the line L and be reflected back from aprepeater point to the talker point W. y y y As has been indicated above, the transmission line L in lwhich the echoes are to be Imeasured isconnected to the line terminals of the hybrid coil H. W'hen ymeasuring echoes under operating conditions, the farend of the 'line L should be terminatedV by a subset, or in some other way there should be a simulation of a normal connection. If the ,object is to studyechoesfrom imbalances at its intermediate points, it would be preferable to terminate the far-end ofthe lin-e by network to reduce echoes from that point. The potentiometer P1, which is connected to the netterminals ofthe coil, is given a resistance which will approximately balance the line impedance. The resistances r1 and 112 have such values that the impedance of the hybridfcoil as seen from the line is ,approxi-v mately'e'qual to the impedance of the line. These resistances furthermore balance each other, and consequently practically none of the echo returned from the line will reach the potentiometer P1. AIf, now, it is desired to measure' the volume of the echo due to the unbalance at anyrepeater point, the commutator faceF is positioned with respect to face F1 so that Contact is made betweenthe brush B2 and the segment S2 after a certain delay following the breaking of contact between brush B1 and segment S1 of face F1.

with segment S2, and the receiver will detect y a portion of the echo reaching point W at a definite time after the original impulse was sent out. 'The impedance of the receiver is made equal to the resistance r2.

If the switch SW:L is thrown to the left, a

the oscillator is detected in the receiver R1,

the fraction being determined by the settingH of the potentiometer P1. i It will now be un` derstood that if the switch SV1 is thrownv alternately to the right and to the left, and

if the potentiometer P1 is adjusted until equal sounds are heard in the receiver R1 for both positions of the switch, the volume ofthe returning echo impressed on the receiver during the contact between brush B2 and segment S2 is readily comparedwith the outgo-Y ing impulse.

If the face F2 is rotated to various positions with respect to face F1 and the operations just described are repeated, an indication may be had of the volume of the echo arriving at the measuring point after a lapse of any given f time from the sending into the line of the alternating current impulses.

It remains to consider the measurement of' listener echoes at the far-end of the Circuit,

represented by point E. At this point the `105.

line L is associated through a transformer T, with a receiver R2 and a commutator arrangement similar to the one employed at the talker end. f The rotatable arms A3 and A4 are connected to a common shaft and designed to be rotated by the motor M1, which is synchronized in any well known manner with the motor M1 at the talker end. Arm A3 is assoated with face F3, which has Yan outer ring ORB and an inner ring IRS. Carried on the The outer Y the rest of the ring. The face F1 carries an Y index 'arm I2, which kis associated with scale SC2, and this face is rotatable with` respect to ',wave arriving Jfrom the line. listening to this receiver now adjusts the .the iacefF3 in any position. It is to be noted that there is an electrical connection between ring IR3 of face F3 and ring OR4 of tace F4. A resistance r3 and a potentiometer P2 are included in the circuit, as shown in the drawing, and the connections ot thereceiver R2 are controlled by a switch SIV2.

It will be understood, of course, that the alternatingfcurrent impulses sent from the oscillator Oat the point WV aree'mployed for the measurements made at point E.

When the brushes B3'y and B4 make contact with the larger ysegments of the outer` rings @R3 and OIL, respectively, the line L is terminated kby the resistance r3, which is approximately equal to the yline impedance. The resistance of potentiometer P2 is equal t-o the resistance r3. When the brush B3 makes contact with the small segment S3 potentiometer'P2 is substituted tory resistance r3. It, now, the

switch SW2 is thrown to the left, the receiver R2 receives a delinite fraction of the The operator face F3 so that theV contact between brush B3 ,and segment S3 occurs at the instant of arri-val of the wave transmitted from the point WV. Throughout the rest or" the rotation of the contact arms the potentiometer P2 and ythefreceiver R2 are disconnected from the line; accordingly, the listener echoes do not affect the receiver R2, with the switch SW2 thrown to the left, during this long contact.

With the face F3 adjusted as described above, the face F 4 is rotated to a position such that contact between4 brush B4 and segment 2 S4 occurs at a definite time after the contact rival ot the original wave. [of this receiver is equal to the resistance r3.

is broken between brush B3 and segment S3 of tace F3. It the switch SW2 is thrownto the right, the receiver vR2 will be connected to the end ot the line L while brush B4 isin con# Atact with segmenty S3; accordingly, the receiver-R2 is aectedby a portion of the echo arriving after a deiinitev delay from the ar- 'Ihe impedance l echo strength.

The'delay between the arrival ofthe orig- "inal wave and the return of the listener echo from any point ot imbalance in the circuit is measured by the displacement of the commutator face F4 with respect to face F3, which vdisplacement is clearly indicated on the scale SC2 by the arm I2.

It the tace F3 is rotated to various positions with respect to face F 3 and the operations described above are repeated, an accurate indication may be had ot the volume of listener echo arriving after a lapse of any given time from the arrival et the original wave.

l/Vhile the invention has been disclosed in one specific embodiment which is deemed desirable, it is to be understood that many modiiications may be made within the true scope ot the invention. For instance, arrangements other than that of the hybrid coil and the potentiometer at the talker end, old and well known in the art,may be employed to assist in the determination of the talker echo volume. Again, any arrangement well known in the art may be employed at point E for comparing the listener echoes withthe di rectly transmitted wave, in place ot the arrangement oi' receiver and potentiometer speciically shown. f

`What is claimed is:

l. In association with a two-way signal transmission circuit, means for sending into the circuit a series of alternating current impulses, means or receiving the currents re turning over the circuit as echoes et said impulses, means associated with said receiving means for'adjustino said means to select certain echoes, and inc icating means associated withl said adjusting means to give the measy ure of the adjustment made, whereby the transmission time ket the selected echoes may be determined.v

2. In association with a twoeway signal transmission circuit, a source ot tone, a receiver, a first commutator adapted to close a circuit .periodically to send the tone from said source into the transmission circuit, a second commutator radapted to close a circuit periodically through said receiver to detectl currents returning over the circuit as echoes oi" the tone currents, and means for rotating the commutator arms together, said second coinmutator havingl its face rotatable with respect to the :taceof said first commutator.

3. In association with a two-way signal 'l ond faces being so segmented and connected that upon the rotation of the commutator -arins said sourceot tone will be connected to the line to send thereover an'inte 1rupted tone and said receiver will be connected to the line at intervals corresponding to the interruptions ot the tone, said second commutator face .being rotatable with respect to said first commutator face, whereby selected echoes arriving over the line may be heard 1n the receiver and the displacement of the second face with respect to t-he first face will indicate tlhe transmission time of the returning currents.

4. In association with a two-way signal transmission circuit, means for sending into the circuit a series of alternating current impulses, means for detecting currents returned over the circuit as echoes oi' said impulses, and a commutator arrangement associated with said sending and said detecting means for timing the sending of the impulses and indicating the delay of the echoes.

5. The method of measuring the transmission time of echoes in a twoway transmission circuit which consists in sending into the circuit series of alternating current impulses, detecting the currents returned over the circuit as echoes of said impulses, and ascertaining the delay of the echoes from the relation between the timing of the impulse sending and the detection.

6. The method of measuring echoes in a two-way transmission circuit'which consists in sending into the ycircuit series ot alternating current impulses, impressing alternately on a detecting device a portion of the outgoing impulses and a portion of the echoes returning to the measuring point, and comparing the two quantities so impressed.

7. The method of measuring echoes in a two-way transmission circuit which consists in sending into the kcircuit series oi' alternating current impulses, impressing alternately on a detecting device a portion of the outgoing impulses and a portion of the echoes returning to the measuring point, eii'e'cting an adjustment tobring the two quantities to equality, and determining the strength of the echoes from the adjustment so made.

.8. In association with a two-way transmission circuit, means for sending into the circuit a series of alternating vcurrent impulses, a detecting means, means for irnpressing alternately on said detecting means a portion of the outgoing impulses and a portion of the echoes returning to the measuring pointV after ak certain delay, and means for comparing the strength ofthe outging impulses and the strength of the returning echoes.

9. In association with a two-way transmission circuit, means for sending into the circuit a series of alternating current imechoes in a two-way transmission circuit which consists in sending into the circuit l from the talker point a series-of alternating current impulses, impressing on a detecting device at the listener point the resulting waves, impressing on said detecting device the echoes arriving at the listener point, determining vthe time elapsing between the arrival of the original wavev and the arrival of the listener echo, and comparing the strength of the original wave and said echo.v

l1. The method v or" measuring listenery echoes in a two-way transmission circuit which consists in sending into the circuit from the talker point a seriesof alternating current ilnpuses, impressing on a detecting device at the listener point a portion of theresulting wave, impressing on said detecting device the echoes arriving at the listener point, eiiect-y j ing an adjustment to Vbring. a portion of the wave to equality with the echoes, and determining the delay of the echoes from such adjustment. y Y

l2. The method of measuring listener echoes in a two-way transmission circuit which consists in sending into the circuit from the talker point a series of alternating current impulses, impressing alternately on a detectj ing device at the listener point a certain raction oi the resulting wave and the echoes arriving at the listener point after a certain delay, and comparing the two quantities so impressed to determine the strength of the echoes.

13. The method l of measuring listener echoes in a two-way transmission circuit which consists in sending into the circuit from the talker point a series of alternating current impulses, impressing alternately on a detecting device at the listener point a certain fraction of the resulting wave and the echoes arrivingY at the listener point after a certain delay, effecting an adjustment to bring the two quantities to an equality, and determining the strength ofthe echoes from the adjustment somade.

In testimony whereof, we have signed our namesto this specification this 27th day'of October, 1928.` Y I Y JOSHUA PAUL SATTERTHWAITE.

- JAMES E. DINGMAN.

pulses, adetecting means, means for impress- H ing alternately on said detecting means a portion of the outgoing impulses and a portion of the echoes returning to the measuring point after a certain delay, and means for adjusting the two quantities impressed on the detecting means to bring said quantities to an equality, whereby the strength of the returning echoes may be determined.

10. The method of measuring listener 

